ptotuningmethods

PTO Tuning Methods

Various ways to obtain reliable and accurate slow-tuning for oscillators

Maybe "PTO" is not the best name for this project, because it covers other slow-tune methods that can be constructed by mere mortals who have limited tools and normal mechanical skills.

The Brass Screw PTO made famous by WA6OTP has been used by many hams, but it does have both advantages and disadvantages. It is simple and easy to construct, however the tuning knob moves in and out from the front panel (some object to this) and mechanical strength is somewhat lacking.

There are ways to build the Brass Screw PTO that do not require the knob to change distance from it's front panel as frequency is changed, and that have much greater resistance to heavy handed operation. There are also other non-inductive ways to achieve very slow tuning rates. A number of methods to accomplish slow-tuning objectives will be added to the panel to the right, as they are developed and evaluated. This is an on-going evolutionary effort, and as such this project may never be "finished".

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A Simple PTO

Shown below are some pictures of a very simple PTO mechanism.

Work In Progress...Info will be added as it is developed.

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While workable, this method was found to require precise mechanical alignment to keep the sliding rod from binding when it was driven fully into the coil form.

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An early attempt at a PTO layout. It does work FB, but has too many parts for efficient and fast construction.

It is just a plastic block, drilled for a 6-32 brass bolt and with 2 inches of 3/8 inch OD PVC tubing fastened to it with hot-melt glue. The plastic block is fastened to the front panel with two self-tapping screws (also 6-32).

If you use 6-32 threaded brass rod for the tuning element, knobs for 1/8 inch shafts will fit on the threaded rod.

Inductor windings are secured to the PVC tube with hot-melt glue.

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While not a true PTO, a slow tuning slide capacitor has been tried and has much the same characteristics as a PTO.

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This is 3/8 inch OD PVC (Basin Tube) hot-melt-glued to the PTO threaded rod mechanism.

Brass nuts were soldered to squares of PCB material. The tuning screw drives in & out via those nuts. This works, but tension on the tuning screw threads is dependent on spacing between the PCB sections. Using a single nut and drilling the outher out to just serve as a bushing might be a better approach.

Here the tuning mechanism hsa been mounted to a pre-cut bezel for the frequency counter and clock displays.

And this gives you an idea what it will look when the receiver is finished.

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Caged Slider PTO Drive

This idea actually works fairly well, but the parts count and requirement for precision manufacture makes it time consuming to reproduce as a one-off method. This design might be suitable for a mass-produced PTO design.

There is a small coil spring under those double nuts . THis pre-loads the slider and helps minimize any backlash.

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